The basic intent of this proposal is to determine whether there are genotypic variations in the effects of aging on learning and hippocampal neurochemistry in two inbred mouse strains (C57BL/6J and DBA/2J and the F1 Hybrid B6D2F1). The effects of aging on associative processes will be investigated by means of a detailed analysis of two types of behavioral habituation: 1) startle habituation and 2) the habituation of exploratory behavior. Beyond various methodological advantages, it is argued that this type of behavioral analysis will provide a means of determining the effects of aging on processes (exploration and habituation) which are of fundamental significance to learning and memory. In addition to differences in behavior, the two parental strains have been shown to differ in terms of hippocampal neurochemistry. Attempts will be made to determine whether hippocampal serotonin and norepinephrine uptake is differentially affected by aging in these different genotypes. Further, attempts will be made to determine whether age-related changes in hippocampal serotonin and norepinephrine uptake are related to the effects of aging on exploration and habituation.